Firestop assemblies are often used to prevent fire and smoke from spreading from one room of a building to an adjacent room. Fire and smoke often spread from room to room through openings between a pipe and a wall through which the pipe passes, and a firestop assembly may be used at the pipe/wall junction to prevent the spread of fire and smoke between rooms. In similar fashion, a firestop assembly may be used at the junction between a pipe and the ceiling of a room, to prevent the spread of fire and smoke from one room to the room above it.
FIG. 1 illustrates a partial cut-away view of a building 10, including a "fire" room 12, and adjacent rooms 14, 16, 18, and 20. A pipe 22 passes through rooms 12, 14, 16, 18, and 20, and a firestop assembly is placed at each of locations A, B, C, D, E, F, and G. If pipe 22 is plastic, no firestop is typically placed at location H, because the heat and smoke from a fire in room 20 rises to the ceiling in that room, rather than dropping to the floor, and thus the firestop assembly at the ceiling of the room below is sufficient.
A fire 30 is blazing in room 12, and the firestop assemblies at B, C, and E operate to prevent the spread of fire from room 12 through the openings between the pipe and the walls, and into rooms 14, 16, and 20, respectively. By containing the smoke and flames within room 12, the danger to persons and property can be minimized because fire fighters must fight a smaller, controlled fire rather than a larger, spreading fire. Thus, firestop assemblies are of considerable benefit in protecting persons, property, and edifices from fire and smoke damage.
A typical firestop assembly 50 is shown in FIG. 2, and comprises intumescent wrap strip 56 and band clamp apparatus 58. Firestop assembly 50 is fitted around the periphery of pipe 52, and abuts wall 54. One or more layers of an intumescent wrap strip 56 (two, in the illustrated assembly) are wrapped around the periphery of pipe 52, and are secured to pipe 52 by band clamp apparatus 58. Wall mount apparatus 60 is also provided, to anchor the firestop assembly to wall 54.
Intumescent wrap strips useful in such firestop assemblies typically comprise polymeric binders, fillers, and intumescent particles. Useful intumescent particles include silicates, expanding graphite, and vermiculite. Typically, such a mixture is compounded with sufficient additives to make a sheet that has suitable expansion, flexibility, and handling characteristics. When subjected to heat or flames, the sheet material expands to seal an opening and forms a strong, insulating char that acts as a barrier to heat, smoke, and flames. A preferred intumescent wrap strip is available under the designation "FS-195" or "FS-195+" intumescent sheet from the Minnesota Mining and Manufacturing Company of St. Paul, Minn. Preferably, the intumescent sheet material is laminated to a restraining layer, such as a metal (preferably aluminum) foil, which acts to control the direction of the expansion of the intumescent sheet. Other materials useful as restraining layers are described in commonly assigned U.S. Pat. No. 4,467,577 (Licht), and include metal screen, paper, cardboard, and rubber or plastic sheets.
The expansion ratio of the intumescent wrap strip (the volume of the wrap strip after exposure to heat, divided by the volume of the wrap strip before exposure to heat, or V.sub.after /V.sub.before) is large (e.g. at least 8.0), and thus the wrap strip tends to expand around the pipe when heat from a fire reaches the wrap strip. Because the expansion of the wrap strip is circumferentially contained (by the restraining layers, or by the band clamp apparatus 58) the intumescent wrap strip expands radially inward--toward the pipe--and firestops, or chokes off, the flow of air and smoke through gap 66 between the firestop assembly and the pipe. During a fire, the intumescent material becomes a rigid char that seals against the passage of smoke, vapors, and water.
Although metal and glass pipe is commonly used for many commercial applications, the use of plastic pipe is increasingly widespread because plastic pipe is inexpensive, tough, nonreactive with most chemicals, and easy to install. For example, pipes made of polypropylene (PP), polyvinyl chloride (PVC), acrylonitrile-butadiene-styrene (ABS), chlorinated polyvinyl chloride (CPVC), and the like may be used as waste pipes in laboratory or factory facilities. However, conventional firestop assemblies are not well adapted to firestop plastic pipes--particular those of large diameter (e.g. 15.2 cm (6 in) or greater)--because plastic pipes tend to collapse when subjected to high temperatures. When a plastic pipe collapses, a sizable gap can be formed between the pipe and the firestop assembly, and conventional firestop assemblies are typically unable to reliably accommodate this reduction in pipe size, which may in turn allow smoke and flames to spread to adjacent rooms. This disadvantage of conventional firestop assemblies can be dangerous to life and to property, and it is therefore desirable to provide a firestop assembly that can reliably firestop both conventional metal and glass pipes, as well as plastic pipes.